The invention relates to a transducer activated tool for contacting workpiece surfaces and directing a fluid adjacent to the workpiece. More particularly, the invention relates to an ultrasonically activated tool such as a dental instrument or insert therefore, including a vibrating tip for contacting tooth surfaces. The tip includes a conduit or passageway for directing a fluid onto the dental or tip surfaces.
Many useful dental instruments employ substantial vibratory motion at a tool tip of the instrument for cleaning, scaling and like operations. The tool tips are designed to produce flexural and longitudinal vibrations with flexural motions of from about 0.02 to 0.2 mm. The tip is typically attached to an electro-mechanical part or section that can be induced to vibrate at high frequency. The instrument is driven by an electronic generator at relatively high frequencies, typically on the order of above 20 kHz, to obtain adequate motion and to minimize objectionable noise since the human hearing threshold is about 18 kHz. The energy generator and related electro-mechanical section maybe any one of several types such as electro-dynamic, piezo electric, or magnetostrictive. Design of the tip and its related electro-mechanical components involves combining a number of parameters to produce mechanical resonances (harmonic vibrations) at the driving frequency to produce amplified mechanical motion, particularly at the distal tip end.
In many operations employing a vibrating tip tool, it is useful and often necessary to have a source of water or other fluid impinging upon the workpiece surfaces and/or tool surfaces in order to cool them or remove debris generated by the work. For example, in dental applications, when an ultrasonically vibrated tip contacts a tooth surface, as required for performing a cleaning operation, the impacting or hammering of the moving tip against the tooth surface produces heat. The patient may experience a pain sensation which can be severe if the operator applies even mild pressure against the tooth while cleaning. Water or some other fluid is usually supplied to the tooth surface in order to remove the heat and minimize pain and possible heat damage to the tooth. In addition, a number of the electromechanical devices utilized in providing a vibrating tip generate heat internally during operation.
An example of an ultrasonic dental tool, wherein a handpiece containing a coil applies an electro-magnetic field to a magnetostrictive insert body to which a tool tip is fixed is described by Perdreaux in Re. 30,536 (Cavitron). In the Perdreaux design, heat caused by electrical and mechanical friction losses within the tool during vibration are dissipated by means of a cooling fluid that flows axially with respect to the tool insert, over the active magnetostrictive element or stack, emerging from an annular space between the insert and the handpiece and being directed toward the working end of the tool. The Cavitron arrangement is such that heat generated by the insert body is absorbed and the fluid directed as a convenient source of irrigating, flushing and/or cooling fluid onto the active tip or workpiece area.
In a number of dental operations, the vibrating tip is guided over and about tooth surfaces by the operator. The tip must be capable of penetrating between teeth and under or below the gingiva or gum line. Generally, the tip must be small in cross-section, ideally having a pointed tip with a tapered cross-section extending about 2.5 to 5 mm back from the distal tip end to allow adequate access between teeth and gingiva.
In addition, the tip is universally curved or shaped to conform to or be compatible with tooth surfaces. Useful tips will curve sufficiently to permit spanning the tooth frontal surface when entrance to abutting surfaces is needed or when access to subgingival zones about the oral cavity are required.
Experience in using such ultrasonically activated and irrigated tips has demonstrated that a combination of tip shape and fluid delivery system must be selected such that the tip is strong enough to support vibrating motion stresses at useable amplitudes. The forming process must be such that minute fractures or other weak points are not introduced into the tip material that might become focal points of breakage during use.
A number of vibrating tools, generally similar to the Perdreaux tool, as described above, are now in dental, medical, veterinary and other uses. These tools employ various designs for directing water or another fluid adjacent to or onto the surfaces being worked upon, as a means of cooling workpiece surfaces and removing debris from the workpiece. For example, a number of ultrasonically activated tools employ separate fluid conduits, external to the instrument itself, for conducting water and other fluids adjacent the tip or onto the workpiece or tip. Kleesattel et al in U.S. Pat. No. 3,076,904 employ a capillary, run externally to the handpiece, with a nozzle formed of a bendable metal extending very near the tip for directing water onto the dental surfaces being worked upon. A difficulty with such arrangements is that the capillary may obstruct free use of the tool tip.
A number of ultrasonic tool tips include internal fluid passageways bored along the longitudinal center axis of the tip component or body. In many such tips, a fluid discharge orifice is formed at the distal end of the tool, for directing Fluid onto the workpiece. Such tip design is described, for example, by Balamuth et al in U.S. Pat. No. 3,924,335 for a piezo electric crystal vibrated dental tool. A difficulty in employing this tip design, is that the tip must generally be of a relatively large diameter, on the order of greater than 1 mm, in order to have a sufficiently strong tip and a passageway that provides an adequate flow of fluid. Such a tip may be too blunt for many dental uses as it does not allow adequate tapering such that the tool thus cannot penetrate small inter-tooth spaces and can damage gums when used subgingivally.
Many tips having internal central axial passageways include a fluid discharge orifice formed by removing a longitudinal lateral portion of the cylindrical wall of the end as the distal tip end is approached, as shown in Haydu U.S. Pat. No. 3,488,851 and Richman U.S. Pat. No. 3,589,012, for example. In Banko U.S. Pat. No. 3,930,173, Robinson U.S. Pat. No. 3,703,037 and Warrin U.S. Pat. No. 5,125,837, the tip is cut away such that remaining lateral walls of the distal tip form a channel for helping direct water discharging from the center axis bore onto the workpiece.
The difficulty with the cutaway designs is that the remaining partially hollowed out end of the tip is rather a fragile shell that cannot support adequate vibrational motion without danger of fracturing. Also, the smaller remaining working surfaces of the tip are subject to more rapid erosion resulting in a shorter useful life of the tool tip than desired.
All of the tips that discharge fluid from the distal end of the tip or close thereto are discharging from a tip at or before a point of high flexural motion, which motion often causes the fluid at this point to spray or form a mist adjacent to the tip and workpiece. Such spraying and misting may prevent fluid from reaching the workpiece area and, instead, dispense it over a relatively wide area, including onto the patient and operator.
Thus, the fluid dispensing characteristics associated with the tips heretofore known in the art are generally deficient due to excessive spray and mist formation that discomfort patients and operators as well as obscuring the working surfaces. In addition, the internal fluid passageway discharge orifices tend to weaken tip surfaces, particularly at the distal end of the tip, causing early failure of the tips through fracture and excessive wear. Tips having axial discharge orifices at the distal end of the tip require significantly more metal at the tip, resulting in blunter tools having less usefulness than desired when contacting confined, smaller surfaces, particularly in dental applications.
It is evident from the state of the art that a new tip design for use in vibratory activated tools would be desirable that can supply an adequate flow of cooling/cleaning fluid to the workpiece without excessive spray and provide an internal passageway and exiting orifice such that the resulting tool tip is capable of withstanding necessary flexural motion of the tip without fracture.